I am sharing a short example of how to display JSON data using ExtJS 4 Store. In previous version of ExtJS, there is a small helper class call JsonStore which is used to simplify creation Stores from JSON data. In ExtJS 4 the class is no longer there. In this example, I am retrieving USGS data as JSON and display it in Grid as shown below.

As shown below in line 20, I use proxy of type JSONP in Ext.data.Store to retrieve the JSON data.

Ext.onReady(function(){
  Ext.define('UsgsList', {
    extend: 'Ext.data.Model',
    fields: [
       {name: 'fid',       type: 'int'},
       {name: 'title',     type: 'string'},
       {name: 'description',  type: 'string'},
       {name: 'link',      type: 'string'},
       {name: 'pubDate',    type: 'date'},
       {name: 'lat',      type: 'string'},
       {name: 'long',      type: 'string'}
    ],
    idProperty: 'fid'
});

var store = Ext.create('Ext.data.Store', {
    id: 'store',
    model: 'UsgsList',
    proxy: {
       type: 'jsonp',
       url: 'http://query.yahooapis.com/v1/public/yql',
    extraParams: {
       q: 'select * from rss where url="http://earthquake.usgs.gov/earthquakes/catalogs/eqs7day-M2.5.xml"',
       format: 'json'
   },
   reader: {
      root: 'query.results.item',
   }
 }
});

function renderTitle(value, p, record) {
   return Ext.String.format('<a href="{1}" target="_blank">{0}</a>',
   value,
   record.data.link
   );
}

var grid = Ext.create('Ext.grid.Panel', {
   width: 700,
   height: 500,
   title: 'USGS - M2.5+',
   store: store,
   loadMask: true,
   disableSelection: true,
   invalidateScrollerOnRefresh: false,
   viewConfig: {
     trackOver: false
   },
   // grid columns
   columns:[{
      xtype: 'rownumberer',
      width: 50,
      sortable: false
   },{
      id: 'title',
      text: "Title",
      dataIndex: 'title',
      flex: 1,
      renderer: renderTitle,
      sortable: false
   },{
      id: 'pubDate',
      text: "Published Date",
      dataIndex: 'pubDate',
      width: 130,
      renderer: Ext.util.Format.dateRenderer('n/j/Y g:i A'),
      sortable: true
   }],
   renderTo: Ext.getBody()
});

// trigger the data store load
store.load();
});